1. Technical Field
The invention relates to enhancing the activity and/or the duration of action of soft anti-inflammatory steroids for topical or other local application.
2. Background Art
Topical or other local application of potent glucocorticoids can produce severe toxic effects such as Cushingoid features, pituitary-adrenal suppression, skin atrophy, immunosuppression, weight gain and inhibition of wound healing. Other kinds of toxic responses, including allergies and cataracts, have resulted from long term use of drugs of this type.
Ophthalmic application of glucocorticosteroids presents additional problems. The protective mechanisms built into the eye allow only small amounts of doses applied to the eye to reach the target sites within the eye; generally, over 90 percent of the total dose will find its way into the general circulation. This in turn leads to serious systemic side effects of the type described above. Moreover, there is a more serious and specific side effect when these drugs are used in the eye, which is an increase in intraocular pressure (IOP). Corticosteroid-induced chronic or acute glaucoma has in fact been reported since the early 1960's. Generally, the corticosteroid is needed only topically to control the inflammation. However, the absorbed steroid is responsible for the serious side effects noted above. It is believed that the effect of the corticosteroid on the aqueous outflow pathway and adjacent tissue glycosaminoglycans (GAG's) is important in the development of glucocorticoid-induced ocular hypertension.
The natural glucocorticosteroids and many of their marketed derivatives are Δ4 and Δ1,4 pregnenes having 21-hydroxy substituents. There are, however, a number of anti-inflammatory Δ4 and Δ1,4 androstenes described in the literature; note, for example, British Patent Specification No. 1,384,372; Phillipps et al. U.S. Pat. No. 3,828,080 and Kalvoda et al. U.S. Pat. No. 4,285,937.
In recent years, soft steroids have been developed in an effort to provide compounds having potent anti-inflammatory activity with minimal systemic activity. One series of soft steroids which is described as having potent anti-inflammatory activity with minimal systemic activity consists of the 17α-carbonates of Bodor U.S. Pat. No. 4,996,335. These compounds include as preferred embodiments haloalkyl 17α-alkoxycarbonyloxy-11β-hydroxyandrost-4-en-3-one-17β-carboxylates and the corresponding Δ1,4 compounds, optionally bearing 6α- and/or 9α-fluorine and 16α- or 16β-methyl substituents. One of these compounds is chloromethyl 17α-ethoxycarbonyloxy-11β-hydroxyandrosta-1,4-dien-3-one-17α-carboxylate, also known as loteprednol etabonate. Loteprednol etabonate is presently marketed in the United States by Bausch & Lomb Pharmaceuticals, Inc. as Alrex® and Lotemax® for ophthalmic use. Other uses of loteprednol etabonate are currently in clinical trials.
Despite the development of steroids having less systemic toxicity, however, there is a serious need for improvement in topical and other local applications. The newer, less toxic, locally/topically active compounds are more expensive to synthesize than the long-established compounds. Moreover, the most potent anti-inflammatory steroids are those which have substitution at the 6, 9 and/or 16-positions and thus also not only are farthest removed structurally from the natural corticosteroids but also have the greatest toxicity. Thus, there is a need for enhancing the activity or duration of action or both of the 17α-carbonate type soft androstenes which lack the 6-, 9- and/or 16-substitution pattern. Further, it would be desirable to allow these steroids to undergo easier metabolism and concentrate them at the desired site of action.
One of the major, inactive metabolites of hydrocortisone is cortienic acid, i.e. 11β,17α-dihydroxyandrost-4-en-3-one-17β-carboxylic acid. Cortienic acid and the corresponding Δ1,4 acid have been previously described as synthetic intermediates useful in the preparation of the soft steroids described in Bodor U.S. Pat. Nos. 4,710,495 and 4,996,335. The 17β-methyl, ethyl and isopropyl esters of Δ1-cortienic acid have been described as putative inactive metabolites of the anti-inflammatory androstene derivatives of WO 97/42214 and Bodor U.S. Pat. No. 5,981,517. The '517 patent also describes the use of Δ1-cortienic acid as a competitor (with [3H]-triamcinolone acetonide as a tracer) for in vitro receptor binding studies of the androstene derivatives of that patent and notes similar studies of loteprednol etabonate. Druzgala et al., J. Steroid Biochem. Molc. Biol., Vol. 38, No. 2, pp. 149-154 (1991), reports earlier in vitro receptor binding studies of loteprednol etabonate and two putative metabolites, Δ1-cortienic acid and the corresponding 17α-ethyl carbonate, in a medium containing 10−5M cortienic acid as competitor, along with [3H]-triamcinolone acetonide as tracer. Druzgala et al. further note that loteprednol itself is intrinsically active, whereas the putative metabolites are indeed inactive. Neither these acids nor their esters have been previously suggested for use in pharmaceutical compositions for the treatment of inflammation because they are not themselves active as anti-inflammatory agents.